Hardening photographic gelatin emulsions and solutions



.Y Patented Nov. 3', 1936 murmur; rno'roanarmc GELATIN EMULSIONS AND summons Samuel E. Sheppard and Robert C. Houck,

Rochester, N. Y., assignors, by mesne assignments, to Eastman Kodak Company, Jersey City, N. J., a corporation of New Jersey No Drawing. Application September 27, 1934, Serial No. 745,754

13 Claims.

This invention relates to photographic materials, and, more particularly, to the hardening of gelatin, either when applied as an emulsion layer on photographic films, plates, or papers, or

5 when applied to paper or other materials in the form of a simple coating or sizing solution.

-In the preparation of photographic emulsions it has been the practice for many years to overcome the tendency of the gelatin to melt, or to swell during processing, particularly at high temperatures, by the addition of various so-called hardening agents, the most well known of which are probably chrome alum and formaldehyde.

Other materials such as acrolein, glyoxal andderivatives of glyoxal, have been proposed for this purpose, but none of these materials has proved to meet all the demands which have :been put upon them, especially from the photographic standpoint. Such aldehyde bodies as glyoxal, for go example, are supposed to posses certain advantages as to speed of hardening and other properties, but all such agents have the disadvantage of increasing the already objectionable brittleness of gelatin layers at low humidities. While this brittleness can be diminished and a temporary softness and flexibility obtained by incorporating certain hygroscopic substances such as glycerol, yet this desirable condition of flexibility is removed in processing when the gelatin emulsion is passed through the usual aqueous processing baths. This is because the glycerol or similar conditioning agent is dissolved out, leaving the gelatin or emulsion in its original brittle condition.

We have now discovered, however, that it is possible to harden and relatively insolubilize gelatin or gelatin emulsions by incorporating therewith a hydroxy aldehyde or aldose. We have found that all of the hydroxy aldehydes up to and including the pentoses and including the hydroxy dialdehydes and hydroxy aldehyde ketones may be successfully employed to harden or insolubilize gelatin emulsions and gelatin layers and enable them to resist relatively elevated temperatures without melting or undue swelling, and in the case of sensitized materials, to do so with less production of fog or desensitizing than the known hardening agents referred to above.

It is accordingly an object of the present invention to overcome the difliculties encountered in the use of known hardening agents and to provide a method whereby gelatin emulsions may be given satisfactory hardening characteristics.

Another object is to provide a photographic emulsion which will resist relatively high temperatures without melting and which will do so without objectionable fogging or desensitizing. A further object is to provide a method of hardening gelatin solutions or gelatin layers in general, whether in the form of photographic emulsions ormerely in the form of a protective coating-applied to paper and similar materials. A still'further object is to provide gelatin layers which will be less subject to the phenomenon known as "after-hardening" in which the melting point of the gelatin rises considerably after storage, particularly storage in a moderately warm atmosphere. Another object is to provide g elatin emulsions of the above characteristics which will process satisfactorily. Other objects will appear hereinafter.

We have found that the above objects may be accomplished by incorporating in the gelatin emulsion or solution one of the hydroxy aldehydes or aldoses up to and including the pentoses, such as glycol aldehyde, glyceric aldehyde, erythritose, arabinose and its isomeric forms, xylose, ribose, and lyxose; a hydroxy dialdehyde, such as tartaric dialdehyde, or a hydroxy aldehyde ketone, such as hydroxy pyroracemic aldehyde.

In the following examples we have set forth several of the preferred embodiments of our inhalide emulsion containing 6-8% gelatin and melting at 32 C. is mixed at a temperature of 4050 G. into 1 c. c. of a 1.25% aqueous glycol aldehyde solution. This mixture is then poured onto a. clean glass plate, or other suitable support, and dried at room temperature.

As illustrating the beneficial effects of the addition of glycol aldehyde to a gelatin in accordance with our invention, the emulsion produced as described above can besatisfactorily processed at 35 C. employing a developing bath, wash water, fixing bath and final wash at that temperature, whereas the untreated gelatin emulsion not containing the hardener melts and runs off the plate at 32 C. (89.6 F.) The hardening appears somewhat-progressive with time, and on storing the emulsion prepared in accordance with the preceding paragraph at room temperature for 16 days, the melting point increases to 95 0. Even under these conditions, glycol aldehyde, for example, does not give rise to serious fog or desensitizing of the emulsion.

Example 2.-26 grams of a photographic silver halide emulsion containing 645% gelatin and melting at 32 are mixed at 40-50 C. with a sufficient volume of a 1% solution of glyceric alde- 5 hyde in water to give an emulsion containing 0.23%, based on the weight of the gelatin, of the aldehyde. This emulsion is then coated on a plate or other suitable support and dried at room temperature. The melting point of the original 10 emulsion is raised from 32 C. to 35 C.. After 44 days storage at room temperature (20 C.) the melting point is raised to about 60 C.

Example 3.-A gelatin emulsion is prepared exactly in accordance with the procedure of Ex- 15 ample 2, except that 1.76% of glyceric aldehyde, based on the gelatin content, was employed. The melting temperature of this emulsion was raised from an original 32 C., to 97 C. After a storage period of 44 days, the melting temperature is 2 raised slightly above 97' C. It will be noted in this case that the hardening eifect of the hydroxy aldehyde compound is somewhat more drastic, but this is due to the fact that a higher mol. percent of the hardening agent is employed for the 25 same amount of gelatin.

Example 4.-26 grams of a photographic silver halide emulsion containing 6-8% gelatin and melting at 32C. is mixed at a temperature of 40-50 C. with a suflicient volume of a 1% arab- 30 inose solution to add to the emulsion 7%, based on the weight of the gelatin, of .the arabinose. The mixture which is found to have an immediate melting point of 34 C., after a six weeks period of storage at room temperature, is found 35 to melt at 89' c. When 14% of arabinose is added to the emulsion, the immediate melting point is also 45 0., while after six weeks storage under the same conditions, the melting point is of the order of 91 0. Both of these emulsions process 40 satisfactorily at temperatures up to 50 C.

'The above examples are, as indicated, merely illustrative and many changes may be made in the various manipulative procedures, temperatures, concentrations, and ingredients within the to scope of our invention, depending on the type of gelatin used and the results desired in the finished product.

Results similar to those illustrated by Examples I-IV above are obtained when xylose, ribose,

50 lyxose and in fact any hydroxy aldehyde up to andincluding a pentose, is employed. While we have chosen to illustrate our invention by reference to certain speciflc hydroxy aldehydes, the broad scope thereof includes the'hydroxy dialde- 55 hydes, typified by the hydroxy dialdehyde known as tartaric dialdehyde, and the hydroxy aldehyde igtones, typified by hydroxy pyroracemic alde- While we have referred to the use of relatively so small amounts of the various hardening agents, these amounts may be varied within wide limits. In general, it may be said that we prefer to use quantities up to 10% of the weight of the gelatin, although we may use considerably smaller -65 amounts and, insome cases, considerably higher amounts of' the hardening agent, the amount used depending largely upon the desired degree of hardening;

Our invention is applicable, not only to the 70 manufacture of photographic emulsions of satisfactory hardening properties, but also to the manufacture of gelatin solutions in general, especially those which are used for producing various coatings or layers on paper, cloth, film and 78 other surfaces.

2 s,oso,e17

Our invention is particularly characterized, not only by the fact that the gelatin can be given a satisfactory degree of hardening, but also by the fact that an emulsion thus hardened retains its original flexibility and will not grow brittle even though a considerable increase in melting point occurs with age (after hardening). Furthermore, since the hydroxylated aldehyde presumably becomes chemically bound to two or more gelatin molecules, it forms part of a colloid network which cannot be leached out in the processing baths as is the case with glycerol and like watersoluble hygroscopic materials heretofore employed for the purpose of giving flexibility. Although an insoluble network is thus produced, the retention of water by the emulsion is not decreased but rather increased. It will thus be seen that we have provided a method of producing a gelatin emulsion which will process satisfactorily at relatively high temperatures and has a substantially constant degree of flexibility.

What we claim is:

1. In the manufacture of photographic articles provided with a hardened gelatin layer of substantially permanent flexibility the step which comprises acting upon said gelatin with a solution of glycol aldehyde.

2. In the manufacture of photographic articles provided with a hardened gelatin layer of substantially permanent flexibility the step which comprises acting upon said gelatin with a solution of glyceric aldehyde.

3. In the manufacture of photographic articles provided with a hardened gelatin layer of substantially permanent flexibility the step which comprises acting upon said gelatin with a solution of. arabinose.

4. An article of manufacture comprising a sheet material having thereon a layer of gelatin of substantially permanent flexibility said layer 40 containing the condensation product of gelatin and a hydroxy aldehyde.

15. A Photographic material provided with a gelatin silver halide emulsion layer of substantially permanent flexibility, said layer containing the condensation product of gelatin and glycol aldehyde.

6. A photographic material provided with a gelatin silver halide emulsionlayer of substantially permanent flexibility, said layer containing the condensation product of gelatin and glyceric aldehyde.

'7. A photographic material provided with a gelatin silver halide emulsion layer of substantially permanent flexibility, said layer contain- '56.

ing the condensation product of gelatin and arabinose.

8. In the manufacture of photographic articles provided with a hardened gelatin layer of substantially permanent flexibility, the step of hardening the gelatin by causing it to react with a hydroxyaldehyde selected from the group con-- sisting of the hydroxyaldehydes up to and including the pentoses. the hydroxy dialdehydes and the hydroxyaldehyde ketones, whereby a condensation product of gelatin and the hydroxyaldehyde is formed.

9. A photographic material provided .with a gelatin silver halide emulsion layer of substantially permanent flexibility, said layer containing the condensation product of gelatin and a hydroxyaldehyde selected from thegroup consisting of the hydroxyaldehy'des up to and including the pentoses, the hydroxyaldehydes and the hydroxyaldehyde hetones.

- 10. A composition of matter comprising a solution of. gelatin containing a hydroxyaldehyde selected i'romthe group consisting of the hydroxyaldehydes up to and including the pentoses, the hydroxy dialdehydes, and the'hydroxyaldehyde ketones, said solution being adapted for the production of a hardened gelatinlayer containing the condensation product of gelatin and the. hydroxyaldehyde.

11. A composition of matter comprising a solution of gelatin containing glycol aldehyde, said solution being adapted for the production 01' a hardened gelatin layer containing the condensation product of gelatin and glycol aldehyde.

- I 12. A composition of matter comprising a solution ot gelatin containing glyceric aldehyde, said solution being adapted for the production 01 a hardened gelatin layer containing the condensation product of gelatin and glyceric aldehyde.

13. A composition of matter composed of a solution oi! gelatin containing arabinose, said solution being adapted for the production of a hardened gelatin layer containing the condensation product of gelatin and arabinose.

SAMUEL E. sHEPPARD. Rosana c. noucx. 

